The study of the action of certain pharmacological agents on muscle related membranes can be approached by using fatty acids as models of drug induced phenomena. Free fatty acids incorporated into the sarcoplasmic reticulum membranes of cardiac and skeletal muscle perturb the functional behavior of these membranes. Certain fatty acids (oleate, myristate) inhibit ATP induced Ca++ uptake while others (sterate, palmitate) activate this function. Utilizing a combination of x-ray and neutron diffraction techniques, the static structural perturbations of the sarcoplasmic reticulum membrane induced by the incorporated free fatty acids may be determined. These studies providing the detailed molecular distribution of the incorporated fatty acids will be correlated with electron microscope images of these membranes. Nuclear magnetic resonance studies will be used to investigate the dynamic structural properties of the sarcoplasmic reticulum lipid bilayer and incorporated fatty acids. Perturbations of the dynamic properties of both the phospholipid headgroup and fatty acyl chains of the sarcoplasmic reticulum bilayer with regards to liquid crystal-gel state and other important parameters will be obtained. These structural studies will allow a determination of the distribution and physico-chemical properties of the incorporated fatty acids in the sarcoplasmic reticulum membrane. A correlation of these structural properties with the energy efficiency ratio (Ca++/ATP) of the membrane should allow a formulation of the mechanism for the action of fatty acids on this membrane and how it relates to both regulation of the contraction-relaxation in muscle and the decrease of contractility and initiation of arrhythmias in ischemic myocardial muscle. In addition, a structural model for the direct action of fatty acids on these membranes may allow an overall mechanism for the actions of anesthetics and other related pharmacological agents on these and related membranes.